a machine or device used for mixing things 搅拌器；混合器 
a food mixer 食物搅拌器 - (British English)
a mixer tap (= one in which hot and cold water can be mixed together before it comes out of the pipe) 冷热水混合龙头
a drink such as fruit juice that is not alcoholic and that can be mixed with alcohol 调酒用的饮料 low-calorie mixers 低热量调酒配料 cocktail mixers 鸡尾酒混合器
- (specialist)
a device used for mixing together different sound or picture signals in order to produce a single sound or picture; a person whose job is to operate this device 声音（或图像）混合器；声音（或图像）混合操作员
Idioms
a good/bad mixer
a person who finds it easy/difficult to talk to people they do not know, for example at a party 擅长／不擅长交际的人